1. Field of the Invention
The present invention relates to a screw for positioning lumbar-sacral fixators which allow a fusion of the vertebral stages damaged during an accident to the spine.
2. History of the Related Art
At the present time, pedicular screws are known, which generally comprise a head provided with a notched surface which lies in a plane parallel to that of the vertical axis of said screw. The head is pierced with a tapped, opening hole which is perpendicular to the axis of the screw. A connecting stem connecting two or more damaged vertebrae comprises at each free end a piece which is pierced with an opening hole. One of the faces of the piece is notched in order to improve contact with that of the pedicular screw. Assembly between the rod and the head of the screw is effected by means of a bolt which is tightened with the aid of a wrench.
It will be noted that tightening of the bolt is effected perpendicularly to the vertical axis of the screw, which considerably complicates assembly. In fact, the free space provided for the passage of the tightening wrench is much reduced.
Moreover, the operator can screw only 1/6 of a turn at once, as the tip of the jaws of the wrench abut against the osseous wall of the transverse processes. In addition, opposite the head of the bolt is located the spine of the vertebra, which prevents the operator from using a screwdriver.
It is a more particular object of the present invention to overcome these drawbacks.